Tone source for telephone systems

Abstract

A tone source is automatically adaptable in operation to generate tones as required for virtually any TDM telephone system in accordance with stored tone samples being defined to meet the requirements of a particular one of the telephone systems. The tone source provides encoded tone samples from a ROM wherein each tone sequence is stored at corresponding sequential address locations. Each sequence is terminated at unique first and last address locations. The last address location is followed by an address location having an end-of-tone code stored therein. A sample of each of the tones is progressively fetched from the ROM in response to each frame occurrence in an associated operating telephone facility. The first address of each sequence is stored at a corresponding index address location in the ROM. In response to each end-of-tone occurrence the index address of the instant tone sample is read from the ROM and used as a starting point for subsequent fetches. Shortly after power-up, the tone source inherently converges into an orderly cyclic operation of providing tones as defined in the ROM.

What is claimed is: 
     
       1. A tone source for providing a plurality of encoded tones for use in a telephone system, said tones being defined in a storage medium having an index page of stored tone index addresses for identifying first storage locations of corresponding tone samples having been sequentially stored therein, comprising: first means for generating sequences of index addresses corresponding to address locations in the index page;   a memory means including storage locations corresponding to the index addresses, a data port, and an address port, the memory means being readable to provide an information word via the data port and writable with an information word directed thereto via the data port at a storage location defined by an instant one of the index addresses being asserted at the address port;   a register means having an output for asserting a registered information word and an input connected with the data port of the memory means, the register means being controllable to register an information word being asserted at its input, and to register an increment of said informaion word;   second means for generating a reinitialization signal in response to a predetermined charcteristic of an information word having been read from the storage medium;   switch means being operative in an absence of the reinitialization signal, for directing a registered information word to the address port of the storage medium to cause an information word of the corresponding storage location to be asserted at the data port of the storage medium, and for directing the increment to the data port of the memory means to cause a corresponding information word to be written at a storage location being defined by the instant index address, and being alternately operative in response to a presence of the reinitialization signal for directing the instant index address to the address port of the storage medium to cause an informaion word of the corresponding storage location to be asserted at the data port of the storage medium, to cause a corresponding information word to be written at the memory means storage location being defined by the instant index address;   whereby tone samples are available from the storage medium for use in the telephone system.   
     
     
       2. A tone source as defined in claim 1 further comprising: an index address bus being connected between an output of the first means and the address port of the memory means;   a data bus being connected between the data port of the memory means and the input of the register means;   a tone address bus being connected to the output of the register means;   and wherein the switch means comprises:   first driver circuits having inputs connected to the tone address bus and outputs connected to the data bus and being controlled to periodically assert the registered information word on the data bus;   a multiplexer circuit having a first input being connected to the tone address bus, a second input being connected to the index address bus, the multiplexer circuit being normally operative for directing the registered information word to the address port of the storage medium, and being operative in response to the reinitialization signal for directing an index address port of the storage medium; and   second driver circuits having outputs connected to the data bus and being responsive to the initialization signal for asserting an information word corresponding to an output of the data port of the storage medium on the data bus.   
     
     
       3. A tone signals circuit as defined in claim 2 further comprising: a logic circuit being connected in series with a sign bit output appearance of the data port of the storage medium, and being responsive to a predetermined bit of each registered information word for generating a sample sign bit being either inverted or non-inverted in accordance with the signal state of the predetermined bit.